Known wooden spring blades of this type normally have a plurality of laminated wood blades with glue layers running parallel with the blade major surfaces. In this context, the blade is typically relatively flat, having two opposite major surfaces, two opposite side edges and two end faces where the major surfaces are significantly wider than the thickness of the side edges. Such a spring blade is e.g. described in Swiss patent 504 860. As a result of this construction, as well as because of the gluing-in of plastic parts, the resilience and durability of the blade is improved and the danger of breaking of the blades is reduced.
In addition , French patent application 2 582 980 discloses a blade which has a plurality of glue layers running perpendicular to the main blade surface. The origin of these blades is plywood technology and they are also partly produced with glued-in plastics.
Sub-body constructions exist in which the blades, unlike in so-called Flex constructions, have relatively small reciprocal spacing. Horizontally glued or laminated wood and vertically glued blades are unsuitable for such sub-bodies, because they are unable to absorb the condensation moisture formed between the blade and a mattress, which leads to grey areas and mould formation below the mattress. This disadvantage is particularly serious if, as is usually the case, additional plastic decorations are stuck onto the surface of the blade. Thus, in the aforementioned sub-body constructions, solid wood blades are used.
However, these known spring blades suffer from three important disadvantages.
1. They are relatively expensive to manufacture because only absolutely flawless raw material is suitable (particularly in constructions where the blade thickness is below 10 mm). Costs are further increased in that sawn timber with a thickness of over 30 mm, not normally available on the market, is required for the production thereof and, apart from the high cost of the material, losses are additionally increased by rough edge cutting.
2. The second disadvantage is that, after cutting from the rough planks, the blades are often warped in the longitudinal direction by the wood tension released, which increases waste and once again increases costs.
3. As a function of the part of the wood, there are also fluctuations in the blade resilience, which is particularly important in constructions having blades with a thickness below 10 mm and this impairs the quality of the sub-bodies produced.